The invention relates to a setting instrument for a tibia part of a knee joint prosthesis.
Knee joint prostheses typically comprise a tibia part which is secured to the tibia and a femur part which is secured to the femur. The tibia part and the femur part are regularly formed metallically. A bearing body with bearing surfaces which is typically manufactured of plastic, e.g. of polyethylene, is arranged between the condylary articulation surfaces of the femur part and the surface of the tibia part which points away from the tibia to the femur. The condulary articulation surfaces of the femur part slide on the bearing surfaces of the bearing body.
In the implantation of a knee joint prosthesis after the surgical opening of the knee the tibia and the femur are prepared with the help of corresponding gauges in such a manner that after the preparation is complete the corresponding prosthesis parts, namely the tibia part on the one hand and the femur part on the other hand, can be secured at the tibia and the femur respectively.
The implantation of the tibia part previously typically takes place in such a manner that orthopedist pre-positions or lightly fixes respectively the tibia part on the prepared tibia by hand and then drives in the tibia stem or a tibia shaft which is connected to the tibia stem further into the prepared tibia. This further driving in typically takes place with the help of an instrument which is placed onto the surface of the tibia part which faces the femur, but which is not fixed there however. Through blows onto the proximal end of this instrument then the tibia stem or a tibia shaft which is connected to the tibia stem respectively is driven into the tibia until the tibia part is secured in the desired manner at the tibia.
This kind of implantation of the tibia part is however rather inconvenient for the orthopedist from the point of view of the handling. He must first pre-position the tibia part by hand on the prepared tibia and then drive the tibia stem or the tibia shaft which is connected to the tibia stem respectively further into the tibia with a not definitively fixable instrument. In this there is the danger in the pre-positioning that the tibia part slips out of the hand of the orthopedist or of another member of the operating personnel and as a result can no longer be used in this operation for reasons of sterility. In the event of a non-central placing on of the instrument during the driving in of an already pre-positioned tibia part an undesirable tipping or skewing of the tibia part can occur, which must be correspondingly corrected in the further driving in.
Here the invention wishes to provide a remedy. In particular it is an object of the invention to avoid the above named disadvantages and to place an instrument in the hands of the orthopedist which facilitates the handling for him during the implantation.
This object is satisfied by a setting instrument such as is characterized by the features of the independent patent claim. Particularly advantageous designs of the instrument result from the features of the subordinate claims.
In particular, this object is satisfied by a setting instrument for a tibia part of a knee joint prosthesis comprising a separate attachment piece for the securing at the tibia part and comprising a hand piece which can be brought firmly into engagement with the separate attachment piece.
Thus prior to the implantation of the tibia part the attachment piece is first secured to the tibia part and then the hand piece is brought firmly into engagement with the attachment piece. This arrangement consisting of a tibia part, an attachment piece and a hand piece then forms a unit which is firmly connected together and which the orthopedist can handle very conveniently. The arrangement is very easy for the orthopedist to grip at the hand piece, so that the danger that the tibia part slips away from the orthopedist or other operating personnel is extremely low. Furthermore, as a result of its good handling ability for the orthopedist the setting instrument permits a precise pre-positioning of the tibia part. Once the tibia part is pre-positioned, the arrangement consisting of the tibia part, the attachment piece and the hand piece can then remain firmly connected together and the orthopedist canxe2x80x94where appropriate after checking the pre-positioningxe2x80x94drive the tibia stem or a tibia shaft which is connected to the tibia stem respectively further into the tibia without having to change the instrument in so doing. He exerts, e.g. with a suitable hammer, blows onto the proximal end of the hand piece, through which the tibia stem or a tibia shaft which is connected to it respectively is driven further into the tibia. The handling is thereby simple and convenient for the orthopedist. Furthermore, both the attachment piece and the hand piece can be simply and reliably sterilized. Moreover, a well defined introduction of the forces into the tibia part also takes place during the driving in.
In one exemplary embodiment of the setting instrument the hand piece and the attachment piece are designed in such a manner that in the secured state they come to lie within the region which is bounded by that surface of the tibia part which points away from the tibia and towards the femur. Thus in this exemplary embodiment no instrument parts protrude beyond the xe2x80x9couter contoursxe2x80x9dof the tibia part in the assembled state. This is particularly advantageous for the implantation since namely the surgical opening of the knee should remain as small as possible, on the other hand however, instrument parts which project beyond the (maximum outer) dimensions could come into conflict during the implanting with soft parts etc. which are arranged around the tibia and could hinder the implantation.
In a further exemplary embodiment the attachment piece has a support part which when the attachment piece is secured lies in contact on that surface of the tibia part which points away from the tibia and towards the femur as well as a application part which is arranged proximally to the support part and can be brought into engagement with the hand piece. One could also say that the attachment piece lies on the bearing surface of the tibia part and has moreover a application part which is arranged proximally to this attachment piece, that the lying in contact on the tibia part and the engagement with the hand piece are thus separate from one another.
In a further development the application part of the attachment piece protrudes beyond the support part when considered in regard to its lateral dimensions, so that a projection is formed. The hand piece is provided at its distal end with a cut-out which receives the support part of the attachment piece during the engagement of the hand piece and the attachment piece and in so doing grips under the projection. This further development enables, after the securing of the attachment piece to the tibia part, a simple pushing on of the hand piece, which then grips under the projection. Through a subsequent bracing of the hand piece with the attachment piece the above described firmly connected together unit consisting of the tibia part, the attachment piece and the hand piece, which is easy for the orthopedist to handle, can be produced in a simple manner. This unit, which is easy for the orthopedist to handle, can for example also be assembled by other operating personnel.
In a further development the hand piece is provided with an abutment which limits the pushing on of the hand piece in the direction of the cut-out during the engagement of the hand piece and the attachment piece. Through this it is prevented that the hand piece can be pushed too far below the projection. For example a correspondingly arranged connection web can be provided as an abutment.
In a further exemplary embodiment of the setting instrument, means for the screwing of the attachment piece to the tibia part are provided for securing the attachment piece to the tibia part. For this, corresponding means (e.g. a thread) must naturally be provided at the tibia part. This kind of securing is not very complicated and expensive and is also simple to carry out as regards the handling.
In a further exemplary embodiment the hand piece has an engagement part at its distal end and proximally to the engagement part a pressure plate which can be displaced in the direction towards the engagement part or away from the latter respectively. The pressure plate is provided with pressure pieces which are firmly connected to the pressure plate and are arranged in the corresponding passage bores in the engagement part of the hand piece. During the displacement of the pressure plate in the direction towards the engagement part the pressure pieces emerge from the passage bores at the distal end and, respectively, during the displacement of the pressure plate they slide in the direction away from the engagement part into the passage bores. Thus for the firm engagement of the hand piece with the attachment piece which is secured to the tibia part the pressure plate is moved in the direction towards the engagement part, which takes place in that the pressure pieces emerge at the distal end from the bores and are braced on the bearing surface of the tibia part. Through this the engagement part is lifted off from the bearing surface of the tibia part and engages firmly under the projection at the attachment piece, through which a firm arrangement consisting of the tibia part, the attachment piece and the hand piece is formed. After the driving in of the tibia part the pressure piece is again moved away from the engagement part, with the pressure pieces sliding back into the bores in the engagement part and the engagement part again coming to lie on the tibia bearing surface and engaging only loosely under the projection, so that the hand piece can be removed again. Then the attachment piece is removed from the tibia part and the implantation of the tibia part is complete. This exemplary embodiment is simple both as regards the constructional cost and complexity and as regards the handling.
In order to drive in the tibia part a striking surface can be provided at the proximal end of the hand piece. Striking impulses can be exerted onto this striking surface with a suitable instrument, for example with a hammer, in order to drive the tibia stem or a shaft which is connected to the tibia stem respectively into the tibia.